dieguez & lopez-gomez 2005

www.elsevier.com/locate/palaeo

Palaeogeography, Palaeoclimatology, P

Fungus–plant interaction in a Thuringian (Late Permian)

Dadoxylon sp. in the SE Iberian Ranges, eastern Spain

Carmen Dieguez a,*, Jose Lopez-Gomez b

aMuseo Nacional de Ciencias Naturales, CSIC, Jose Gutierrez Abascal, 2. 28006 Madrid, SpainbInstituto de Geologıa Economica-Dpto. Estratigrafıa, CSIC-UCM, Facultad de Geologıa, Universidad Complutense, 28040 Madrid, Spain

Received 9 January 2004; received in revised form 16 November 2004; accepted 24 June 2005

Abstract

This report describes an anatomical and taphonomical study of a large, exceptionally well-preserved Late PermianDadoxylon

sp. trunk. The specimen, found in siliciclastic red bed sediments of fluvial origin of the Landete Formation, Iberian Ranges,

eastern Spain, includes the first described fungus–plant interaction for this time interval in Europe. This finding is all the more

significant since a bfungi-enriched layerQ, recently reported in sediments of different continents corresponding to the end of the

Permian, has been related to a world-wide crisis, whereby fungi were responsible for the breakdown of massive amounts of

vegetation–already suffered by a possible catastrophic event or events–leading to a global drop in photosynthesis. The well-

known humid, temperate climatic conditions of the Late Permian sediments and the sedimentary environment represented by the

Landete Formation would have favoured the proliferation of fungi which was probably unaffected by any other significant biotic

activity. Fungal activity is likely to have started soon after the fall of the plants, indicated by the good preservation state of areas of

the trunk unaffected by the fungal infection. Later diagenesis suggests different fluid migration stages, clearly conditioned by the

original anatomical characteristics of the trunk and the results of fungal activity. Physical signs left by the enzyme action of wood-

decay fungi can be recognised in the fossilised wood. Using this information and sedimentological data, we reconstructed the

taphonomic processes incurred by the specimen, including both biostratinomic and diagenetic stages.

Ullmania sp. and pollen grains such as Lueckisporites and Nuscoisporites dulhuntyi produced by species of Late Permian

Walchiaceae or Ullmanniaceae that did not cross the Permian-Triassic boundary were also found in levels stratigraphically

below the fossil specimen; none occurred above the trunk site. This flora and fungal activity could relate this level of Iberian

Permian sediments to the level or one of the levels associated with the worldwide Late Permian crisis and fungal proliferation.

D 2005 Published by Elsevier B.V.

Keywords: Permian-Triassic boundary; Iberian Ranges; Wood-decay fungi; Dadoxylon

0031-0182/$ - see front matter D 2005 Published by Elsevier B.V.

doi:10.1016/j.palaeo.2005.06.031

* Corresponding author.

E-mail address: [email protected] (C. Dieguez).

1. Introduction

Recent advances in research into the Permian-

Triassic include the demonstration that different

alaeoecology 229 (2005) 69–82

C. Dieguez, J. Lopez-Gomez / Palaeogeography, Palaeoclimatology, Palaeoecology 229 (2005) 69–8270

events of considerable palaeoenvironmental signifi-

cance might be related to the end of Permian or to

the Permian-Triassic transition. These events mainly

involved changes in atmospheric characteristics,

Fig. 1. Upper part: geographical and geological location of the study area.

Massif. Lower part: palaeogeographical sketch of the western Tethys area

marked volcanic events, superanoxia in oceans, and

mass marine and continental extinctions (see Isozaki,

1994; Retallack, 1995; Hallam and Wignall, 1997;

Kozur, 1998; Yin and Tong, 1998; Looy et al.,

Numbers indicate the main present-day basin, ranges and the Iberian

during the Late Permian. Modified from Ziegler (1988).

C. Dieguez, J. Lopez-Gomez / Palaeogeography, Palaeoclimatology, Palaeoecology 229 (2005) 69–82 71

2001; Twitchett et al., 2001 among others). Many of

these events are still unresolved in most of the world

mainly due to an incomplete sedimentary record, the

particular lithological characteristic and the lack of

adequate fossils.

Over the last decade, several new techniques have

been developed to address this question. These meth-

ods show a large spectrum of possibilities for eluci-

dating the main factors responsible for the general

changes that occurred during this period of time,

including terrestrial and extraterrestrial causes.

Among the proposed terrestrial causes is a chain of

general changes occurring in response to severe mod-

ifications in the atmosphere as a result of the rapid

eruption represented by the Siberian traps basalt

floods (Renne et al., 1995; Kozur, 1998; Wignall,

2001). As a consequence, the collapse of terrestrial

ecosystems could have initiated a worldwide fungal

event at the top of the Permian, as suggested by Eshet

et al. (1995), Visscher et al. (1996) and Steiner et al.

(2003).

The present paper is based on a detailed study of a

spectacular specimen of Thuringian (Late Permian)

age consisting of a well-preserved fossil trunk show-

ing signs of interaction with fungi and found in a

middle zone of the Landete Formation, Iberian

Ranges, in the east of Spain (Fig. 1). In the Iberian

Ranges, the succession of Permian and Triassic sedi-

ments is represented by classic siliciclastic red-bed

deposits of continental origin (Sopena et al., 1988;

Lopez-Gomez et al., 2002). The Late Permian sedi-

ments of the SE Iberian Ranges have been well-

known since the middle 20th century (Richter and

Teichmuller, 1933; Boulouard and Viallard, 1971;

Viallard, 1973; Virgili et al., 1983, 1980; Lopez-

Gomez and Arche, 1993; Arche and Lopez-Gomez,

1999), however, until now, few well-preserved floral

elements have been found in these sediments.

Many publications have dealt with fossil woods of

different age, but few specimens have appeared so

close to the Permian-Triassic boundary (PTB) as the

trunk described here. There are also few descriptions

of fungal–plant interactions in the Late Permian (Tay-

lor et al., 1994; Visscher et al., 1996; Taylor and

Taylor, 1997; Steiner et al., 2003, among others),

and only exceptional references to fossil woods bio-

degraded by saprophytic fungi (Stubblefield et al.,

1985; Taylor and Stubblefield, 1987; Stubblefield

and Taylor, 1988; Taylor, 1990; Taylor and Osborn,

1992). The specimen described here is the first Per-

mian-Triassic wood of its kind described in Europe.

We present an anatomical and taphonomical

description of the fossil trunk, the possible signifi-

cance of its interaction with a fungus and the general

characteristics of the sedimentary environment. The

main aim of this study is to improve our current

understanding of the palaeoenvironmental and

palaeogeographical characteristics of this enigmatic

time interval, in a continental area not far from the

westernmost coast of a prograding Tethys Sea that

reached the Iberian Basin during the early Anisian

(Middle Triassic).

2. Geological setting and stratigraphy

The present-day Iberian Ranges are part of an

intracontinental fold chain in the east Iberian micro-

plate, formed by Cenozoic inversion of the intracra-

tonic Iberian Basin. This basin represented part of a

complex of rift systems that developed during the

Permian in central and western Europe (Fig. 1) and

underwent several synrift phases until the beginning

of the Jurassic (Sopena et al., 1988; Lopez-Gomez

and Arche, 1993; Salas and Casas, 1993; Arche and

Lopez-Gomez, 1996; Van Wees et al., 1998; Lopez-

Gomez et al., 2002).

The fossil trunk was found 4 km south of Landete

village, in the southern area of the Iberian Ranges

(Fig. 1), where the Late Permian sedimentary record

comprises two formations of alluvial origin (Arche

and Lopez-Gomez, 1999): the Boniches Conglomer-

ates and the Alcotas Siltstones and Sandstones, from

base to top, respectively. The trunk was found close to

the top of a fine-medium grained subarkosic sand-

stone body, approximately in the centre of the Alcotas

Formation (Fig. 2). The Alcotas Formation crops out

in a large area of the Iberian Ranges, with generally

good outcrops normally related to anticline cores. This

unit lies conformably on the Boniches Formation or

unconformably on the Ordovician quartzites or slates

and is up to 125 m in thickness. In the upper contact,

the Canizar Formation overlies the Landete Formation

by means of a sharp contact that probably represents a

hiatus or mild unconformity (Lopez-Gomez and

Arche, 1993).

Fig. 2. Detailed stratigraphical section of the Landete Formation in the Landete area and location of the fossilised trunk.


2.1. The age of the fossil trunk and the Alcotas

Formation

Discerning the age of Permian sediments repre-

sented by siliciclastic red beds has always been pro-

blematic. For example, the Karoo Basin (McLeod et

al., 2000) is one of only a few examples in the world

that permit timing the evolution of fossil groups in red

beds by isotope contrasting. It is even more difficult to

find sections to compare the biotic evolution of marine

and terrestrial realms in the same area, as in the case of

some Jameson Land series, East Greenland (Twitchett


et al., 2001; Stemmerick et al., 2001). A further limita-

tion is that, in most of the world, the Permian-Triassic

transition shows substantial sediment gaps.

Only a few papers have described the Late Permian-

Triassic chronostratigraphy of the Iberian Ranges in

detail (Boulouard and Viallard, 1971; Sopena et al.,

1988, 1995; Doubinger et al., 1990; Lopez-Gomez et

al., 1998, 2002, among others), yet more remarkable is

that the Scythian (Lower Triassic) was never dated in

the Iberian Peninsula. Indeed, the incompleteness of

the Permian-Triassic fossil record is an interesting

matter of discussion (see Twitchett, 2001). The avail-

able chronostratigraphical data were mainly derived

from palynological assemblages, and many of these

assemblages appear in the Landete Formation (Bou-

louard and Viallard, 1971; Arche et al., 1983; Virgili et

al., 1983; Lopez-Gomez and Arche, 1986; Doubinger

et al., 1990) or its lateral equivalent formations

(Ramos and Doubinger, 1979; Sopena et al., 1995).

This would indicate a Thuringian (Late Permian) age

for this unit based on the presence of: Nuskoisporites

dulhuntyi, Lueckisporites virkkiae, Paravesicaespora

splendens and Klausipollenites schaubergeri.

The trunk was found 65 m from the base of the

section (Fig. 2), in which three palynological assem-

blages at 25 m, 59 m, and 62 m, from base of section,

have been described (Boulouard and Viallard, 1971;

Doubinger et al., 1990). The fossil trunk is therefore

considered Thuringian in age. Other trunk remains,

less than 80 cm long were found dispersed along the

base of the same level.

Palynological assemblages of both underlying

(Boniches Conglomerates) and overlying (Canizar

Sandstones) formations of the Landete Formation indi-

cate Thuringian (Late Permian) and Anisian (Middle

Triassic) ages, respectively (Doubinger et al., 1990).

However, we have to consider that the underlying

Boniches Formation association also shows Autunian

forms in its uppermost part, such as Vittatina and

Potoniesporites, indicating an early Thuringian age,

and that the assemblage of the overlying Canizar For-

mation was also obtained at the top of this formation.

2.2. Sedimentary characteristics and depositional

environment

The Alcotas Formation is made up of red siltstones

and clays, and associated lenticular sandstones,

including conglomerate bodies. The maximum thick-

ness is 170 m. Sandstones are arkoses, their clay

fraction consisting mainly of illite (Alonso-Azcarate

et al., 1997). Total mineralogy shows a substantial

punctual increase in hematite and dolomite in the

upper third of the formation (Fig. 2). Sandstone and

conglomerate bodies in the formation consist of

upward-thinning and -fining sequences, generally

less than 1 m thick. When well developed, as in the

section in which the fossil trunk was found, these

bodies show concave-upwards bases and do not gen-

erally exceed 550 m in lateral extension. Thinner

bodies have a somewhat flatter base and extend lat-

erally beyond several tens of metres. Palaeocurrents

towards the SE are persistently indicated.

The general sedimentary characteristics of the

bodies examined indicate that the Alcotas Formation

was deposited by sandy low-sinuosity braided rivers

isolated in floodplains that evolved to sandy mean-

dering and sheetflood distal braided deposits. The

sediments of the Landete Formation were deposited

in a basin consisting of a series of half-grabens with

the main sediment source located in the Iberian Massif

at the NW of the basin. These sediments were trans-

ported south eastwardly by axially orientated rivers

(Arche and Lopez-Gomez, 1996).

Descriptions of both the sedimentological charac-

teristics of the Landete Formation and its sedimentary

environment are detailed in Lopez-Gomez and Arche

(1993), Arche and Lopez-Gomez (1996, 1999) and

Lopez-Gomez et al. (2002).

During the deposition of most of the Alcotas For-

mation, the climate is believed to have been warm

and temperate, accompanied by a monsoon circula-

tion (Arche and Lopez-Gomez, 1999). Although there

are obvious difficulties in comparing recent and

ancient climates, it should be noted that, according

to palaeomagnetic and palaeogeographic data, the

basin under study was located near the equator during

the Late Permian (Ziegler, 1988; Fluteau et al., 2001).

This hypothesis is also supported by the plant

remains found and the styles of fluvial sedimentation

of the Landete Formation indicating transport and

deposition by running water. On the other hand, an

increased hematite content in the middle part of the

studied section (Fig. 2), particularly abundant in red-

dish surface horizons in acidic sandy soils (Retallack,

2001), along with a decrease in the plant remnant


content of sediments, could tentatively indicate a

remarkable oxidation stage for this period of deposi-

tion, although other already existing factors could

also have been at work.

3. Anatomy and taxonomy of the fossil trunk

The fossil log is a very well-preserved silicified

specimen that was first described in Dieguez and

Lopez-Gomez (1999). Its present size is 6.2 m long,

1.1 m in diameter (Fig. 3). At least, signs of one in situ

original branch clearly related to this trunk were found

in the substratum sandstone level analysed here. The

specimen is housed in Museo de las Ciencias de

Castilla-La Mancha (Cuenca, Spain).

The fossil specimen is comprised of a decorticated

secondary xylem, with uniform and homoxylic wood

and no growth rings, showing clear signs of silica

Fig. 3. The studied fossilised trunk in the Landete section outcrop.

Hammer in the middle part of the trunk for scale. See also Fig. 2 for

the stratigraphical location of the trunk in the section.

permineralisation processes and is dark-brown

coloured.

3.1. Anatomical description

The anatomy of the specimen was established by

examining fourteen thin transverse, radial and tangen-

tial sections of the secondary xylem. These thin sec-

tions were made using the conventional cutting and

polishing methods for optical microscopical study

being deposited in the Museo Nacional de Ciencias

Naturales-CSIC (Madrid, Spain).

Cross-section (Figs. 4a and 5a–e). Growth rings

absent. Xylem rays uniseriate, about 25 Am width,

separated by a variable number of files of tracheids,

from 2 to 7 (average 3). Tracheids thin-walled, about

25 ım width, of variable shape (from isodiametric to

oval or polygonal in transverse section) depending on

compression and the proximity to other tracheids,

from 87.5 to 125 Am in size and arranged in regular

radial files. Neither the resin ducts nor the bordered

pits on the end wall of tracheids have been observed.

Nevertheless, there are pairs of bordered pits in the

wall of tracheids with torus located in the middle of

the membrane.

Tangential section (Figs. 4b, c, g and 5f). Rays

are mostly uniseriate ranging from 4 to 18 cells in

height. The upper and lower ends of the rays are

suddenly tapering which is a typical araucariaceae

structure. Ray cells thin-walled (about 12.5 Am)

varying in size in the same ray from 12.5 to 62.5

Am in diameter. Tangential bordered pits present at

the end of tracheids.

Radial section (Fig. 4d–f). Tracheids showed a

large, circular lumen with absence of spiral thickening

in their radial walls. Bordered pits in radial walls

(from 12 to 39) oval to rounded, about 40 Am in

diameter, arranged usually in one file (rarely two)

according to an araucaroid pattern. If uniseriate they

are arranged contiguously. When biseriate, they are

arranged alternately and become uniserate at the ends

of tracheids.

3.2. Taxonomy

Based on these general anatomical features, we

were able to classify the wood specimen as a Dadox-

ylon sp. of the Coniferophyta division comprised of a

a b c

d e f g

100 µm 100 µm 100 µm

100 µm100 µm100 µm100 µm

Fig. 4. (a) Uniserate xylem rays and tracheids arranged in regular radial files, 31786, TS. (b) Short linear uniseriate rays cells, MNCN343,TLS.

(c) Long uniseriate rays and tangential bordered pits, MNCN342, TLS. (d) Uniseriate araucaroid bordered pits arranged contigously, 35078,

RLS. (e) Uniseriate bordered pits at the end of tracheids, 31874, RLS. (f) Biseriate bordered pits arranged alternately, 31874, RLS. (g) Ends of

rays tapering suddenly and tangential bordered pits (arrow), MNCN342, TLS.

Fig. 5. (a) Contiguous walls of two tracheids showing bordered pits with torus in central position (arrow) and diverse stages of delignification

31786, TS. (b) Lignin decay with separation of walls layers due to the fungus attack in an early stage of lignin removal (arrows), 31786, TS. (c)

Advanced stage of delignification. Only some zones of the tracheids walls and persistent wall corners can be observed. Tracheids are perceptible

as impressions except in the central area. (d) Early stage of decay. Note the different degree of decay in the different zones of wood, 31786, TS.

(e) Later stage of wood-decay. Persistent wall corners and middle lamellae of thacheids located close to a decay pocket, 31786, TS. (f) Early

stage of delignification of tracheids with zones without tangential walls (arrows) MNCN342, TLS.



single, homogeneous wood type (homoxylic). The

anatomy of the specimen closely resembles the sec-

ondary xylem of the extant Araucaria brasiliana Rich

(Araucariaceae).

The general anatomical characteristics of the trunk,

including homoxylic wood and bordered pits of the

araucaroid type, are consistent with those presented by

the genus Dadoxylon Endlicher and Araucarioxylon

Krauss. Literature on gymnosperm fossil wood

records a comprehensive discussion on nomenclature

of these two genera and diverse criteria for the taxo-

nomic attribution of specimens have been established.

These criteria were based on different aspects viz.: age

of the specimens (Seward, 1917; Stewart, 1983), pre-

sence of uniseriate or multiseriate rays (Maheshwari,

1972), presence of pith and primary xylem (Lepe-

khina, 1972), and presence/absence of araucaroids

remains in the same horizon from which the specimen

of wood comes (Seward, 1917). More recently, new

nomenclatural revisions of the homoxylous woods

have been made (Philippe, 1993; Philippe et al.,

1999; Bamford and Philippe, 2001) mostly based on

Mesozoic material.

Following the criteria established by Seward

(1917, p. 249) and Stewart (1983, p. 344), the speci-

men has to be ascribed to the genus Dadoxylon End-

licher. According to these criteria, wood specimens

showing araucaroid bordered pits collected from

Palaeozoic sediments should be denoted as such. In

addition, Seward (1917, p. 250) advocated the assign-

ment to Dadoxylon for those fossil wood specimens

collected in a horizon in which unmistakable repre-

sentatives of the Araucariaceae are lacking. The fossil

record of Dadoxylon is difficult to establish since

different systematic fossil classification systems have

been applied such that some Dadoxylon trunks have

been attributed to Araucaroxylon, or vice versa. The

Dadoxylon record and related palaeoxylologic studies

for the Iberian Peninsula are restricted to citations by

Broutin (1978) for the Lower Permian of Rıo Viar

(Seville, Spain), and by Garcıa Gimenez et al. (1983)

for the Mesozoic of Palmaces de Jadraque (Guadala-

jara, Spain).

3.3. Remarks

The specimen’s secondary xylem shows a replace-

ment by silica in fossilisation processes. Although

preservation is exceptional, in some areas the com-

plete destruction of the cell walls of tracheids can be

observed (Fig. 5b–f). These areas are associated with

other zones of the wood in which cell dissociation in

the tracheids is patent. This type of wood decay (Fig.

5b) is extraordinarily similar to that shown by speci-

mens of Araucaroxylon from the Permian and Triassic

of Antarctica (Taylor and Stubblefield, 1987, Fig. 2;

Stubblefield and Taylor, 1988, Fig. 2f).

In addition to this decay, the wood also contains

spaces (pockets) lacking conductive elements sur-

rounded by cells with secondary walls clearly dis-

torted by lignin decay, also comparable to those

described by Stubblefield and Taylor (1988, Fig. 2f),

and pockets surrounded by tracheids, modified in

shape, at different stages of lignin decay (Fig. 5b,

c). These patterns of decay in the secondary wood

can be attributed to the actions of saprophytic fungi as

described by Taylor and Osborn (1992). This latter

work (Fig. 7 thereof) also describes a Permian speci-

men of Araucaroxylon with cell corners persisting in

tracheids after delignification by fungi. Similar results

have been observed in our specimen (Fig. 5c, e).

Saprophytism of wood is very common today, but

the fossil record of this interaction between plants and

fungi, known as wood rot, is extraordinarily scarce,

and the few existent references almost exclusively

relate to trunks of similar age to the specimen

described here (Taylor and Stubblefield, 1987; Stub-

blefield and Taylor, 1988; Taylor, 1990; Taylor and

Osborn, 1992).

Recent analysis of the effects of fungal infection of

plant remains (conducted on a Cenomanian conifer)

indicate that distorted cell walls show substantial

amounts of hydroxysuccinic acid and functionalised

benzoic compounds that were interpreted as degra-

dation products of lignin by fungi (Nguyen Tu et al.,

2000). The decomposition of organic matter by micro-

bial or fungal action may have also contributed to

significant amounts of polysaccharides found in Late

Permian sediments in the Dolomites in northern Italy

(Sephton et al., 1999). The findings of both these

studies indicate that this fungal activity could be

more intense than observed in more ancient sediments.

The activity of saprophytic fungi, particularly that

of basidiomycetes, leads to lignin degradation, trans-

forming organic C to inorganic C by an enzyme action

known as wood rot (white rot and white pocket rot).


Ligninolytic enzymes have a broad specificity and

decay processes occur in an obligate aerobic environ-

ment (Pointing, 2001). Initially the fungus focuses its

enzyme activities on the middle lamella, which sepa-

rates the wood’s cells leading to their final destruction

(Fig. 5a–f). This action affects cellulose and the lignin

which makes up the tracheids. Lignin biodegradation

mechanisms in living material have been mainly

explored by evaluating the activity of basidiomycete

fungi (Leonowicz et al., 1999; Steffen et al., 2000;

Papinutti and Forchiassin, 2000). There are, however,

some recent studies on fossil material (Nguyen Tu et

al., 2000) from Cretaceous conifers that describe the

action of ascomycete fungi that act on the lipid frac-

tion. Further research efforts have explored potential

factors affecting the ligninolytic activity of saprophy-

tic fungi (Godio et al., 2000) and their action on

organopollutants of similar chemical structure to lig-

nin (Pointing, 2001).

Analogous decay patterns have been observed in

fossil and living wood, suggesting a similar decay

mechanism at the biochemical level (Stubblefield

and Taylor, 1986). Thus, correlations may be made

among the mechanisms and factors affecting the

extant wood and those that affected the fossils. Lignin

degradation is mainly attributable to basidiomycetes

but there are also a few ascomycete and deuteromy-

cete fungi capable of wood rot decay. Based on the

anatomical alterations and type of the key pattern

observed, we attribute this decay to the action of

saprophytic fungi. However, given this indirect evi-

dence and the lack of fossilised fungal remains such as

mycelia, hyphae or spores, it is not possible to identify

the agent producing the decay.

4. Taphonomy of the fossil trunk

4.1. Biostratinomic processes (transport and abrasion)

After the death of the tree and fall of the trunk,

necrolytic processes may have been induced by

fungi, given the appropriate humid and temperate con-

ditions of the area for their proliferation, probably

along with high CO2 concentrations (Fluteau et al.,

2001; Retallack, 2001; Kurschner, 2001). High con-

centrations of atmospheric CO2 would stimulate the

tree’s physiology, development and growth, by enhan-

cing leaf photosynthesis, suppressing plant respiration

and reducing transpiration. Biomass production, litter-

fall would also be enhanced, as microbial biomass

proliferation (especially fungi) and the activity of

decomposers such as fungi increased (Ceulemans et

al., 1999; Osborne and Beerling, 2002). The quality of

preservation of areas unaffected by saprophytic fungi,

indicate the trunk was not substantially affected by

further biotic activity (of bacteria and/or fungi). Bear-

ing this in mind along with the decomposition time of a

trunk (Martin, 1999, Table 5.3), we could argue that

fungal infection began very soon after the fall of the

tree.

Although the extent of fungal infection cannot be

determined in the specimen studied and consequently

the decay quantified, it is evident that, in larger or

smaller measure, the physical characteristics of the

wood would be affected by the disappearance of lignin.

In addition, altering the anatomy of the wood, the

action of wood rotting fungi also modifies the physical

properties of the wood, e.g. their water-holding capa-

city (Benito, 1943; Boddy, 1986; Norden and Paltto,

2001).

Sedimentological data indicate general low energy

shallow water fluvial systems during the deposition of

the trunk (Arche and Lopez-Gomez, 1999). It is very

possible that the channel capacity of these fluvial

systems was insufficient to transport the trunk over

a long distance and it is likely that these channels were

abandoned very soon.

There are no indications of further modification to

the physical characteristics of the trunk such as resis-

tance to compression, flexibility and hardness and

stiffness, with the exception of the absence of defor-

mation or breakage, from which we could infer that

the trunk was not severely altered.

4.2. Fossil diagenetic processes

Diagenetic analysis of the fossil trunk indicates

several linked stages that clearly started as soon as

the trunk became buried. Its relatively well-preserved

internal details could indicate that decay was early

inhibited and that mineralization progressed rapidly

due to fluvial dynamics inducing the quick burial of

the trunk. Similar cases were described by Fielding

and Alexander (2001) in Australia for recent and

Permian fossil trees. The rapid subsidence of the

Fig. 6. (a) Micro- and macroquartz crystals showing preferentia

fluid migration routes controlled by the cell organisation of the

fossil trunk. (b) Secondary macroquartz crystals of triangular

shape (top left) and perpendicular veins reflecting a later stage of

crystal growth (lower right).


Iberian Basin during Thuringian times has also been

reported (Salas and Casas, 1993; Arche and Lopez-

Gomez, 1996; Van Wees et al., 1998). Mineralization

is largely dependent on the depositional environ-

ment, although the precise chemistry of this process

is not well understood. It seems that partial decay is

needed for silica preservation, and early diagenetic

silicification is also a prerequisite for exceptional cases

of microorganism preservation. However, further ad-

vanced decay would have caused the complete or

nearly complete destruction of internal details except

for those comprised of more complex macromolecules

(Allison, 1988; Allison and Briggs, 1991).

Two quartz forms were differentiated by petrogra-

phical analysis of thin sections: megaquartz and

microquartz (Fig. 6a,b). The microcrystalline mor-

phology of the latter indicates the replacement of

original chalcedonic quartz. Both megaquartz and

microcrystalline quartz infill pore spaces, while gen-

eral diagenetic modifications give rise to megaquartz

through dissolution–reprecipitation reactions.

The outer area of the secondary xylem of the

trunk’s internal structures were the best preserved,

since penetration of liquid silica probably com-

menced in this region. The log’s inner areas were

therefore progressively partly sealed from further

penetration, and decay probably progressed leading

to destruction and to the formation of cavities filled

with crystalline quartz.

Fluid migration in a generally acid medium prob-

ably conditioned the replacement of the original ele-

ments of the plant cell structure by microquartz in an

initial stage of diagenesis. This first fluid migration

stage could have formed the red-brown iron oxide

coating in the spaces between the walls of the trac-

heids, wherever iron was readily available in stream

water. A later stage is indicated by the appearance of

microquartz, probably both by replacement and pore-

infill processes, as suggested by the straight bound-

aries of the crystals or triple points where growth

meets, which are highly characteristic of pore-filling

cements (Adams et al., 1984). Macroquartz crystals

could indicate a subsequent diagenetic stage. This

form of quartz newly occurred in the xylem rays,

where recrystallisation was still possible.

Crystal growth in microfractures of the specimen is

also suggestive of several stages. An early stage prob-

ably involved refill of microquartz in synsedimentary

l

microfractures that were probably formed during the

readjustment of the trunk during the early stages of

burial. Iron oxide was also probably deposited on the

microfracture walls during these processes, while

silica would have migrated along these microfrac-

tures. Microfractures that cross-organic structures

show a clear later stage of recrystallization. These

newly generated microfractures would be refilled

after the migration of silica-saturated fluids once

again via the newly created free spaces.

Polycrystalline quartz with crystals elongated in

preferred orientations and sutured boundaries between

crystals were relatively common in the fossilised

trunk. These probably appeared as a result of stress


conditions due to changes in pressure and temperature

during several later phases of the Alpine Orogeny

(Salas and Casas, 1993) and the appearance of micro-

folds and microfractures could have promoted fluid

circulation. In contrast, the frequent finding of a well-

preserved cell structure suggests a limited degree of

compaction or its prevention in part by early miner-

alisation, such that tissue permeation could take place

(Carson, 1991).

Although there are several possible sources of

silica through geologic time (see Carson, 1991), in

the case of the particular lithology of the Landete

Formation, some of the silica may have been derived

from detrital quartz, as well as from the transforma-

tion of the clay minerals themselves, such as the

alteration of montmorillonite to kaolinite during sub-

aerial weathering (Alonso-Azcarate et al., 1997).

5. Discussion

The Permo-Triassic boundary marks a period in

which known species numbers showed a fall of

around 20% and in which the sedimentation of

plant-bearing rocks was low, at least in Europe

and North America (Niklas et al., 1983). The Late

Permian saw the adaptive radiation of the seed

plants that culminated in the gymnosperm-domi-

nated Mesozoic.

Known stratigraphic ranges of natural conifer taxa

recognised in Late Permian flora assemblages from

western, central and southern Europe, such as Wal-

chiaceae or Ullmanniaceae, do not cross the PTB.

Species of these Late Permian families produced

pollen grains corresponding to several palynological

species such as Jugasporites, Lueckisporites, or Nus-

coisporites dulhuntyi in the case of species of Orti-

seia. These were a prominent component of the

xerophilous Late Permian flora of the southern Alps

(Poort et al., 1997). In a vertical interval of less than

5 m, the Landete Formation shows some of the last

Permian levels known to date in Iberia. These levels

also contain the conifers Dadoxylon sp. and Ullman-

nia sp. and the palynological species L. virkkiae and

Nuscoisporites sp. (Doubinger et al., 1990).

Conifer dieback may have provided the organic

resource supply for fungal proliferation and has been

well described in Europe, North America, Asia,

Africa and Australia for the Late Permian (Eshet et

al., 1995; Visscher et al., 1996; Looy et al., 2001;

Steiner et al., 2003), where fungi probably adapted

and responded quickly to the environmental distur-

bance. Thus, the dieback of arboreal vegetation may

have been a worldwide event that affected the terres-

trial biosphere, irrespective of the local nature of

climatic and flora changes (Poort et al., 1997; Looy

et al., 1999). In several sections of the Southern Alps

(Visscher and Brugman, 1986; Cirilli et al., 1998;

Visscher et al., 2001), Israel (Eshet et al., 1995)

and South Africa (Steiner et al., 2003), there are

reports of the disappearance of the gymnosperm-

dominated palynoflora of the Late Permian L. virk-

kiae from a claystone horizon almost exclusively

containing abundant fungal remains and carbonised

terrestrial plant debris. We do not exclude the possi-

bility that the above-mentioned 5 m interval of the

upper Landete Formation corresponds to part of a

large-scale loss of standing biomass in the western-

most Tethys as one of the stages in the worldwide

biotic crisis of the Late Permian.

If adverse conditions at the end of the Permian,

such as acidification, anoxia or any other cause or

causes (see Kozur, 1998; Wignall and Hallam, 1992;

Erwin, 1993; Hallam, 1994) that altered the develop-

ment of plants, allowing the opportunistic prolifera-

tion of fungi, this competition must have also

conditioned the different plant groups. If the cause

or causes suggested above led to a general rise in

atmospheric CO2 levels (Yin and Tong, 1998;

Kozur, 1998), the global vegetation mass would initi-

ally increase leading to reduced soil nutrients.

6. Conclusions

We report the discovery of an extremely well-pre-

served fossilised trunk (6.2 m long, 1.1 m wide) of

Thuringian (Late Permian) age in the Landete Forma-

tion, SE Iberian Ranges, Spain. The general anatomi-

cal features of the fossil correspond to those shown by

the genus Dadoxylon Endlicher of the Coniferophyta

Division and are similar to those of the present-day A.

brasiliana Rich (Araucariaceae).

Detailed petrographical study permits to observe

different processes such as decay processes due to

fungal activity. These processes include the destruc-


tion of lignin, indicating the activity of saprophytic

fungi, an interaction previously described for the Per-

mian of Antarctica. These processes could also be

related to those worldwide fungal events at the top

of the Permian as a consequence of the collapse of

terrestrial ecosystems and the increase of organic

material proceeding of the dieback of forests.

Sedimentological approaches indicate that fluvial

system was insufficient to transport the trunk over a

long distance. Fossil diagenesis processes indicate

early dissolution–reprecipitation reactions and differ-

ent stages of recrystallisation.

Acknowledgements

This paper is a contribution to PICG Projects 458,

465 and PB98-0488 and BTE2002-00775 of the

Spanish Ministry of Science and Technology. We

thank Gilberto Herrero for preparing the thin sections.

Helpful reviews by Sharon Klavins and an anon-

ymous referee improved the content of the article.

Special thanks are extended to B.K. Ferguson, A.

Arche and F. Surlyk for constructive comments. We

also thank Ana Burton for the revision of the first

English version.

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